An aircraft nacelle is a structure that surrounds an aircraft engine and broadly includes an inner cowl surrounding the engine and an outer cowl positioned outward of the inner cowl, forming an air duct or fan duct therebetween. Air flows in a forward to aft direction through the fan duct and out through an opening at an aft end of the nacelle, sometimes referred to as a nozzle.
In some aircraft applications, it is desired to vary the area of the nozzle. For example, Variable Area Fan Duct Nozzle (VAFN) technology is used on high-bypass turbofan engines to modulate airflow and pressure within the fan duct. In a turbo fan engine there are generally two flow paths—a core and a bypass or fan duct. A majority of the air goes through the bypass and produces most of the engine's thrust. The VAFN is located in the aft portion of the bypass duct and varies fan exit nozzle area during take-off and landing via various actuation means for mechanically expanding aft openings of the nacelle or providing additional openings proximate to the aft end of the nacelle. By increasing or decreasing the effective exit area of the fan duct nozzle, several potential benefits may be realized, such as greater noise reduction or greater fuel efficiency. Varying the area may also be required to enable certain engine technology, such as geared turbofan (GTF) engines. However, the electrical and mechanical components of various VAFNs generally add undesired weight to the aircraft.